At present, the surgical correction of deformities of the spinal column involves a surgical procedure for the insertion of fixation implant devices, such as pedicle screws or hooks, to each vertebra followed by application of external forces to achieve the desired correction of the shape of the spinal column and attachment of the said fixation devices to rigid rod-like elements to achieve permanent stabilisation of the involved part of the spinal column. Bone graft is also added to achieve permanent fusion of the same part of the spinal column.
Previous devices for correcting spinal deformities have involved the fixation of bone screws which connect to rods via pivoting connections, for example as described in WO-A2-2007/014119. Also, the use of ratchet mechanisms with spinal implants is known from WO-A2-2008/057861, WO 2007/143709 and EP-A2-1051947. Although these arrangements increase the versatility and ease of application of implants used for spinal fixation, the application of all currently used implants and methods for surgical correction of deformities of the spinal column results in the amount of correction of the deformity achieved during the surgical procedure often being limited. Furthermore, during application of all current implants and methods for surgical correction of deformities of the spinal column the entire correction is achieved during the surgical procedure and no further degree of correction is possible thereafter as the involved part of the spinal column is permanently fused. The consequences of this are the permanent loss of spinal motion and subsequent increase of the mechanical loads to the adjacent mobile spinal segments frequently leading to wear of these segments.
One device, described in US-A1-2005/0261770, has various arrangements of interconnecting vertebral supports including pivoting and sliding arrangements between the components in an attempt to avoid fusion and permanent loss of the mobility of the spinal column. However, such implants cannot be used as spinal deformity correcting devices as no means for adjusting the relative position of the vertebrae is provided. Other devices are described in US-A1-2006/155279, EP-A1-0667127, US-A1-2003/191470, U.S. Pat. No. 5,951,555, U.S. Pat. No. 5,672,175 and GB2412320 which include springs, flexible rods or other force-generating means, such as memory alloys, attempt to prevent development of the deformity or even to gradually correct a deformity of the spinal column. Although such disclosed devices are able to facilitate the development of corrective forces between parts of the spinal column most are passive and are unable to provide for the progressive correction of spinal deformities assisted by active movements of the human body. The present invention addresses this issue.